Method and device for controlling the speed of an internal combustion engine

ABSTRACT

A device and a method for controlling an internal combustion engine, in particular for regulating the speed of the internal combustion engine, are described. At least one first governor, specifies a first manipulated variable based on a comparison between a first setpoint value and an actual value. At least one second governor specifies a second manipulated variable based on a comparison between a second setpoint value and the actual value. The first manipulated variable is limited to a first manipulating range and the second manipulated variable is limited to a second manipulating range.

BACKGROUND INFORMATION

[0001] The present invention relates to a method and a device for controlling an internal combustion engine, in particular for regulating the speed of the internal combustion engine.

[0002] Methods and devices for controlling an internal combustion engine, in particular for regulating the speed of the internal combustion engine, are known. In such systems, there is interaction between at least one idle speed governor and one manipulated variable, that of the driver command, which is detected via a gas pedal position. In the process, a controlled variable corresponding to the driver command torque, which is determined by the gas pedal position, and a manipulated variable of a governor corresponding to the torque of the idle speed governor, work together. The controlled variable, i.e., the driver command torque, should override the idle speed governor, i.e., the torque of the idle speed governor. Overriding means that the idle speed governor does not have any effect on the controlled variable if the driver command torque is greater than the torque of the idle speed governor. As a result, the speed may be increased when the driver steps on the accelerator. The governor is supposed to prevent the speed from falling below the idling speed. In this case, if the driver does not accelerate, the governor overrides the controlled variable.

[0003] This means that for different functionalities, a permissible speed interval should be maintained using regulation, in the course of which a controlling intervention should be possible, in particular by the driver.

[0004] It is particularly advantageous when at least one first governor specifies a first manipulated variable on the basis of a comparison between a first setpoint value and an actual value, and at least one second governor specifies a second manipulated variable on the basis of a comparison between a second setpoint value and the actual value, and the first manipulated variable is limited to a first manipulating range and the second manipulated variable is limited to a second manipulating range.

[0005] This means that first governors that deliver the manipulated variables only within a particular manipulating range are provided, while second governors deliver manipulated variables only within a second manipulating range. Both first and second governors are preferably designed as proportional governors or as proportional and integral governors.

[0006] It is particularly advantageous when the first manipulated variable is limited in such a way that the parameter to be regulated decreases and the second manipulated variable is limited in such a way that the variable to be regulated increases. In the example of a governor that regulates this via the quantity of fuel, this means that the first governor may only reduce the quantity of fuel and the second governor may only increase the quantity of fuel.

[0007] Depending on the requirements set for the governor, different setpoint values are specified. It is particularly advantageous when the setpoint values are specified as a function of the operating state. Here, the first setpoint value is always greater than or equal to the second setpoint value.

[0008] In order to avoid an undesired behavior of the control circuit, in case both control units provide a manipulated variable, the manipulated variable representing the greatest absolute-value change is used for control. In this case, it is particularly advantageous for the manipulated variable of the other governor, i.e., of the governor representing the smallest absolute-value change, to be frozen.

[0009] Of particular importance furthermore are the implementations in the form of a computer program having program code means and in the form of a computer program product having program code means. The computer program according to the present invention has a program code means for performing all the steps of the method according to the present invention when the program is executed on a computer, in particular a control unit for an internal combustion engine of a motor vehicle. In this case, the present invention is thus implemented through a program stored in the control unit so that this control unit provided with the program represents the present invention in the same way as the method for whose execution the program is suitable. The computer program product according to the present invention has program code means stored on a computer-readable storage medium in order to execute the method according to the present invention when the program product is executed on a computer, in particular a control unit for an internal combustion engine of a motor vehicle. In this case, the present invention is thus implemented through a storage medium so that the method according to the present invention may be executed when the program product or the storage medium is integrated into a control unit for an internal combustion engine, in particular of a motor vehicle. In particular, an electric storage medium, such as a read-only-memory (ROM), an EPROM, or even an electric permanent memory, such as a CD-ROM or DVD, may be used as a storage medium or as a computer program product.

[0010] The present invention is explained in the following on the basis of an embodiment illustrated in the drawing, whose figures show:

[0011]FIG. 1 a block diagram of the process according to the present invention,

[0012]FIG. 2 a detailed illustration of the control structure, and

[0013]FIG. 3 a flow chart to illustrate the process according to the present invention.

[0014] A device for controlling an internal combustion engine is illustrated in FIG. 1. The internal combustion engine is labeled 100. Various sensors that record the different signals are positioned on the internal combustion engine. In particular, a speed sensor 110 is provided, which delivers a signal NI that corresponds to the measured speed of the internal combustion engine.

[0015] Furthermore, different control elements 120 that influence the power output of the internal combustion engine, and consequently, the speed of the internal combustion engine, are positioned on internal combustion engine 100. In particular, control elements 120 are provided, which control the torque provided by the internal combustion engine, in particular via the quantity of fuel injected.

[0016] Control element 120 is subjected to control signals preferably from a control unit 130. Output signal NI of sensor 110 likewise reaches control unit 130. Furthermore, signals from other sensors 140 as supplied to control unit 130. They include in particular a signal FP that characterizes the driver command. A gas pedal position sensor is in particular used for this purpose.

[0017] Based on driver command FP and actual speed NI, this control unit computes a control signal to be supplied to control elements 120. To regulate and/or control the speed, in particular in diesel engines, an idle speed governor, a working speed governor, a vehicle-speed governor, a final speed governor, a maximum speed governor, a general governor and/or a governor, are provided. In particular the final speed governor, the working speed governor, and/or the vehicle-speed governor are used for maintaining an upper speed limit. The idle speed governor ensures that the speed of the internal combustion engine does not drop below the idling speed. The vehicle speed governor causes the speed to maintain a certain value that corresponds to the desired vehicle speed. The working speed governor similarly ensures that the speed does not drop below a desired working speed.

[0018] The final-speed governor and the maximum-speed governor ensure that an upper speed limit is maintained. The final-speed governor ensures in particular that a maximum permissible speed is not reached. The maximum speed regulation ensures that a speed corresponding to a desired maximum speed or a permissible maximum speed is not exceeded. The special case in which the upper speed limit corresponds to the lower speed limit exists in particular when, in an automated gearbox, a speed determined for the gearshift operation is adjusted through the general governor. The same also applies to a governor when the driver setting of the driver command is interpreted as a setpoint speed. This applies in particular to special applications in the commercial vehicles.

[0019] Each of the mentioned functionalities is normally implemented by its own governor. In general, these governors have different points of intervention. Problems occur when several governors are intervening simultaneously. This results in instabilities. Furthermore, problems appear when switching from one functionality to the other. An example is the replacement of the idle speed control by a working speed control. In this case, the problem is for the actuator intervention of the first governor to be suitably accepted in the second governor. This means that the initialization of the individual governors during the transition is problematic.

[0020] A speed interval governor which is therefore proposed according to the present invention, prevents the speed interval from being exited irrespective of the controlling intervention of the governors. In the special case of interval width 0, the governor fully compensates for the control intervention to maintain the desired speed. In the general case of an infinite interval width, the governor behaves neutrally, if at all possible, when the speed is found within the interval limits on account of the controlling intervention or on account of other interfering variables. If the interval limits are suitably interconnected, i.e., the setpoint values are suitably specified, such a speed governor is in a position to implement all or only a part of the above-mentioned functionalities.

[0021] The advantage here is that resources may be saved in the control unit as well as in development and calibration, since only one governor is required. Improvements to be made for one functionality are also of benefit to the other functionalities. In the event of competing functionalities, clear prioritizing may take place on the level of determining the setpoint value. Overlapping intervention of several governors is out of the question. The replacement of one functionality by another is simpler to ensure. Initialization must take place only in one governor, and not in several governors.

[0022] According to the present invention, a speed interval governor is implemented by a parallel structure of two governors. The two parallel governors preferably have a PI character. One of the two governors regulates to an upper interval limit as upper setpoint value NSO. The other governor regulates to the lower interval limit as lower setpoint value NSU. In each of the signal paths, the actuator intervention is limited in such a way that the permissible setpoint value interval is not exited.

[0023] Assuming a positive point-to-point behavior, i.e., an increase of the manipulated variable results in an increase of the controlled variable, this means that for the two control paths, the control path for the lower speed limit only intervenes to increase the speed. The lower limit of its actuator intervention is consequently 0. The actuator intervention permissible at the current operating point preferably functions as an upper limit. The control path for the upper speed limit may only intervene to decrease the speed. The upper limit of its actuator intervention is 0. The instantaneous control value for the actuator intervention, for instance, may be used as a lower limit. This ensures that if the upper interval limit is exceeded, the controlling actuator intervention may be compensated by the governor intervention. Through the combined effect of the two control paths, speed-increasing as well as speed-decreasing interventions are possible. This also applies when the upper and the lower interval limits are the same, i.e., upper setpoint value NSO and lower setpoint value NSU are the same. With these setpoint values, a pure speed regulation may be implemented using the same structure. Thus, for instance, overriding the control value in a transmission control is possible.

[0024] A corresponding governor structure is illustrated as a block diagram in FIG. 2. Elements already described in FIG. 1 are marked with the same reference numbers. Output signal NI of speed sensor 110 reaches a first P-component 120 and a first I-component 122 through a first node 115. Furthermore, through a second node 125, this signal reaches a second P-component 130 and a second I-component 132.

[0025] A first output signal NSO of a setpoint value setting 135 is applied to the second entrance of first connecting point 115, while output signal NSO of setpoint value generator 135 is applied to second node 125.

[0026] The output signal of the first integral component 122 reaches a node 142 through a first limiter 140. The output signal of first P-component 120 is applied to the second input of node 142. Via a second limiter 144, the output signal of second integral component 132 reaches a node 146, to whose second input the output signal of second proportional component 130 is applied.

[0027] The output signal of node 142 is received by a first manipulated variable limiter 150, whose output signal MO reaches reactive current compensating circuit 160. A second manipulated variable limiter 155, whose output signal MU likewise reaches reactive current compensating circuit 160, receives the output signal of node 146. Via a node 162, the output signal of reactive current compensating circuit 160 reaches signal limiter 165, whose output signal M is received by control element 130, or which a signal is computed and supplied to control element 130.

[0028] The output signal of a node 170, which receives output signal W of a weighting generator 172 and the signal of a differential component 174 is applied to the second input of node 162.

[0029] The output signal of the manipulated variable limiter 165 furthermore reaches a start value generator 180, whose signal is in turn received by a first start value generator 182 and a second start value generator 184. Output signal MO of the first manipulated variable limiter is furthermore supplied to first start value generator 182. Similarly, output signal MU of second manipulated variable limiter 155 is supplied to second start value generator 184.

[0030] Integral component 122, first limiter 140, and proportional component 120 form a first governor that regulates the speed to upper interval limit NSO. Manipulated variable limiter 150 limits the output signal of this governor to negative values, i.e., this governor only has only torque-reducing intervention. This means that the upper threshold of this limiter assumes the value 0.

[0031] Proportional component (P-component) 130 and integral component (I-component) 132, as well as second limiter 144 form a second governor, which regulates the speed to lower interval limit NSO. Here, limiter 155 is designed in such a way that this governor may only perform torque-increasing interventions, i.e., the output signal MO of this governor branch is limited in such a way that the smallest possible value is 0.

[0032] Starting from these two manipulated variables MU and MO, reactive current compensating circuit 160 then selects the corresponding manipulated variable. This is corrected in node 162 using the weighted output signal of D-component 174. The use of D-component 174 results in improved quality of control. Particularly in the event of setpoint value jumps or transient behavior at an interval limit, this D-component has a positive effect on the governor behavior. This correction takes place only in selected operating states.

[0033] If the difference between lower interval limit NSO and upper interval limit NSU is small, i.e., if the difference between lower setpoint value NSU and upper setpoint value NSO is small, in particular when the two setpoint values are equal, it must be prevented that both control paths become dynamically active at the same time in certain operating states, i.e., that both specify a torque command. This is ensured via reactive current compensating circuit 160. Control interventions of both control paths, in particular in the same direction, i.e., with a change of control intervention in the same direction, are to be avoided since this results in both control amplifications being added. If each control path is properly laid out, overlapping of both control paths in the same direction would result in an unstable behavior due to high circuit amplification.

[0034] The following procedure is used for impressing the control interventions onto the parallel control circuits. If changes in the same direction are made to the actuator interventions, the path that exhibits the change that is greater in absolute value is dynamically impressed, i.e., used to drive the control element. The integrator of the other path is set through corresponding start value generator 182 or 184 in such a way that the intervention last effective for the current system deviation appears again. The inactive path is therefore virtually frozen.

[0035] A corresponding procedure is shown in FIG. 3.

[0036] In a first step 300, blocks 120, 122, 140 and 142 determine manipulated variable MO of the first path and blocks 130, 132, 144, and 146 determine manipulated variable MU of the second path. Subsequently in step 310, difference DMO between new manipulated variable MO and manipulated variable MOA calculated during the last computation is determined. Difference DMO of the second control circuit, based on current value MU and the preceding MUA, is similarly determined. Subsequent query 320 examines whether difference DMO of the first control circuit is greater than 0, i.e., whether manipulated variable MO increases. If this is not the case, i.e., the controlled variable decreases, query 330 examines whether difference DMU is greater than 0. This means that it is examined whether the controlled variable of the second control circuit likewise increases. If this is the case, i.e., the first manipulated variable decreases and the second manipulated variable increases, step 340 follows. If query 330 recognizes that second manipulated variable DMO likewise decreases, i.e., it is less than 0, step 350 follows. If query 320 recognizes that the first manipulated variable increases, i.e., difference DMO is greater than 0, query 335 which examines whether the difference DMU of the second manipulated variable is greater than 0 follows. If this is the case, which means that second manipulated variable DMO also increases, step 350 likewise follows. If the second manipulated variable is less than 0, meaning that the first manipulated variable increases and the second manipulated variable drops, step 340 likewise follows.

[0037] This means that if the changes in the control interventions are in an opposite direction, i.e., one increases and the other decreases, step 340 follows. In other words, the two manipulated variables are added to form starting value M. If the manipulated variables do not change in an opposite direction, meaning that both manipulated variables increase or both manipulated variables decrease, the absolute value of the change in each manipulated variable is determined in step 350. Variable BMO, which corresponds to the absolute variable of variable DMO, and variable BMU, which corresponds to the absolute variable of variable DMU, are preferably determined. Query 360 examines whether variable BMO is greater than variable BMU. If this is the case, i.e., the absolute value of change in the manipulated variable of the first control circuit is greater than the absolute value of change in the second control circuit, the manipulated variable MO of the first control circuit in step 370 is used for control. At the same time, the I-component of the second control circuit is frozen to its previous value, i.e., the I-component is set at the value MUA.

[0038] If variable BMO is not greater than variable BMU, i.e., the absolute value of change in the second manipulated variable is greater than the absolute value of change in the first manipulated variable, the manipulated variable of the second control circuit in step 380 is used for control and I-component 122 of the first control circuit is occupied by variable MOA.

[0039] This means that in this advantageous embodiment, the manipulated variable exhibiting the greatest change is used for control if both governors provide a manipulated variable.

[0040] D-component 174 is active only in certain operating states. When D-component 174 is switched off, its intervention is taken over by I-component s 122 and/or 132 in order to ensure a continuous characteristic of manipulated variable M.

[0041] Start value generator 180 divides the manipulated variable of D-component 174 into parallel paths.

[0042] The procedure is as follows: First, it is examined whether the manipulated variable MD of the D-component, in particular the weighted manipulated variable, is greater or less than 0. If manipulated variable MD is greater than 0, as much MD as permitted by upper limit 0 is allocated to integral component 122. The remainder is allocated to integral component 132.

[0043] The control concept described is generally usable on all systems that have a controlling intervention on the manipulated variable of the governor. The procedure is not limited to speed regulation, but may also be used for other regulations. In the reactive current compensating circuit according to block 160, other strategies are also conceivable. For instance, a change-over of the two paths may take place not on the basis of the absolute value of the manipulated variable, but on the basis of the system deviations, in particular the absolute value of the system deviations.

[0044] Instabilities in the event of simultaneous intervention of both parallel paths may also be avoided through selected parameters, for example lower gain factors or through dynamic decoupling.

[0045] Instead of two parallel paths, the functionality, in particular when using a computer, may take place through multiple computation of a path using different parameters and/or limiting values.

[0046] Other strategies are also conceivable for the initialization in block 180. Quantity-increasing interventions may be performed in the second path, i.e., in particular in integrator 132. Similarly, torque-reducing interventions may be performed in the first path, in particular in integral I-component 122. The initialization is preferably performed in such a manner that, if at all possible, no path reaches the limitation range.

[0047] Instead of the PI-governors, other control structures may be used, in particular containing additional components or alternative components.

[0048] The described example of an embodiment involves the torque as the manipulated variable. Instead of this variable, other variables that represent the torque may also be used. In particular, the procedure may be performed on the injection amount, the throttle valve position, the angle of ignition for the control rod position or gate valve position in edge-controlled systems. 

What is claimed is:
 1. A method of controlling an internal combustion engine, in particular of regulating the speed of the internal combustion engine, having at least a first governor, which specifies a first manipulated variable based on a comparison between a first setpoint value and an actual value, having at least a second governor, which specifies a second manipulated variable based on a comparison between a second setpoint value and the actual value, wherein the first manipulated variable is limited to a first manipulating range and the second manipulated variable is limited to a second manipulating range.
 2. The method as recited in claim 1, wherein the first manipulated variable is limited in such a manner that the variable to be regulated decreases, and the second manipulated variable is limited in such a manner that the variable to be regulated increases.
 3. The method as recited in claim 1 or 2, wherein the first setpoint value is greater than or equal to the second setpoint value.
 4. The method as recited in one of the preceding claims, wherein, in the case where both control units provide a manipulated variable, the manipulated variable having the greatest absolute-value change is used for the control.
 5. The method as recited in claim 4, wherein the manipulated variable with the smallest absolute-value change is frozen.
 6. The method as recited in one of the preceding claims, wherein, in certain operating states, the manipulated variable is additionally influenced by a governor exhibiting at least a differential behavior.
 7. A device for controlling an internal combustion engine, in particular for regulating the speed of the internal combustion engine, having at least one first governor, which specifies a first manipulated variable based on a comparison between a first setpoint value and an actual value, having at least one second governor, which specifies a second manipulated variable based on a comparison between a second setpoint value and the actual value, having means that limit the first manipulated variable to a first manipulating range and the second manipulated variable to a second manipulating range.
 8. A computer program having program code means for executing all steps from any of claims 1 through 7 when the program is executed on a computer, in particular on a control unit for an internal combustion engine.
 9. A computer program product having program code means that are stored on a computer-readable storage medium for executing the method as recited in any of claims 1 through 7 when the program product is executed on a computer, in particular on a control unit for an internal combustion engine.
 10. A digital storage medium, in particular a diskette having electronically readable control signals, which is able to cooperate with a programmable computer system in such a way that a method is executed as recited in any of claims 1 through
 7. 